src/posix.mak: Link against libstdc++ explicitly

[CyberShadow]

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[CyberShadow]

Thanks though I'd have waited for Brad's autotester just in case.

[yebblies]

This should not have been necessary... I don't know why it wasn't automatically added just by using g++ to link.

[CyberShadow]

It could be something distro-specific, or it could be because of some of the hacks I had to do to work around other distro-specific issues (e.g. the libcurl/--as-needed one).

[CyberShadow]

Oh yeah, I had CC point to gcc not g++.

Well, we might as well keep this in case anyone does this too. Is the CC variable commonly used for C/C++ compilers interchangeably, or is there another convention for an environment variable name for C++ compilers?

[HK47196]

or is there another convention for an environment variable name for C++ compilers?

CXX, CC is strictly for the C Compiler, this applies to *FLAGS aswell.
currently, D's makefiles stomp all over environmental variables anyways.